03-tongue & thyroid

8/3/2019 03-Tongue & Thyroid

http://slidepdf.com/reader/full/03-tongue-thyroid 1/35

THYROID GLAND & TONGUETHYROID GLAND & TONGUE

Dr. Mujahid KhanDr. Mujahid Khan



Development of ThyroidDevelopment of Thyroid

The thyroid gland is the first endocrine gland toThe thyroid gland is the first endocrine gland to

develop in embryodevelop in embryo

It begins to form about 24 days after fertilizationIt begins to form about 24 days after fertilization

It develops from a median endodermalIt develops from a median endodermal

thickening in the floor of a primordial pharynxthickening in the floor of a primordial pharynx

Thickening soon forms a small outpouchingThickening soon forms a small outpouching

called thyroid primordiumcalled thyroid primordium




As the embryo and tongue grow, the As the embryo and tongue grow, the

developing thyroid gland descends in thedeveloping thyroid gland descends in the

neck, passing ventral to the developingneck, passing ventral to the developing

hyoid bone and laryngeal cartilageshyoid bone and laryngeal cartilages

For a short time the thyroid gland isFor a short time the thyroid gland is

connected to the tongue by a narrow tube,connected to the tongue by a narrow tube,

the thyroglossal ductthe thyroglossal duct




At first the thyroid primordium is hollow but it At first the thyroid primordium is hollow but itsoon becomes solid and divides into right andsoon becomes solid and divides into right andleft lobesleft lobes

The two lobes are connected by the isthmus of The two lobes are connected by the isthmus of the thyroid glandthe thyroid gland

Isthmus lies anterior to the developing secondIsthmus lies anterior to the developing secondand third tracheal ringsand third tracheal rings

By seventh week it assumes the definitive shapeBy seventh week it assumes the definitive shapeand has reached its final site in the neckand has reached its final site in the neck




The thyroglossal duct has normallyThe thyroglossal duct has normallydegenerated by seventh weekdegenerated by seventh week

The proximal opening of the thyroglossalThe proximal opening of the thyroglossalduct persists as a small pit in the tongue,duct persists as a small pit in the tongue,the foramen cecumthe foramen cecum

A pyramidal lobe extends upward from the A pyramidal lobe extends upward from theisthmus in about 50% of peopleisthmus in about 50% of people




The pyramidal lobe may be attached to theThe pyramidal lobe may be attached to the

hyoid bone by fibrous tissue or smoothhyoid bone by fibrous tissue or smooth

muscle, the levator of thyroid glandmuscle, the levator of thyroid gland

The pyramidal lobe and the associatedThe pyramidal lobe and the associated

smooth muscle represent a persistent partsmooth muscle represent a persistent partof the distal end of the thyroglossal ductof the distal end of the thyroglossal duct



Histogenesis of ThyroidHistogenesis of Thyroid

The thyroid primordium consists of a solid mass of endodermal cellsThe thyroid primordium consists of a solid mass of endodermal cells

The cellular aggregation later breaks up into a network of epithelialThe cellular aggregation later breaks up into a network of epithelial

cordscords

By the tenth week the cords have divided into small cellular groupsBy the tenth week the cords have divided into small cellular groups

A lumen soon forms in each cell cluster and the cells become arranged A lumen soon forms in each cell cluster and the cells become arrangedin a single layer around the lumenin a single layer around the lumen

During the eleventh week colloid begins to appear in these structures,During the eleventh week colloid begins to appear in these structures,called thyroid folliclescalled thyroid follicles

Iodine concentration and synthesis of thyroid hormones can beIodine concentration and synthesis of thyroid hormones can bedemonstrateddemonstrated



Thyroglossal Duct Cysts &Thyroglossal Duct Cysts &

SinusesSinuses Cyst may form anywhere along the courseCyst may form anywhere along the course

followed by the thyroglossal duct during descentfollowed by the thyroglossal duct during descent

of the primordial thyroid gland from the tongueof the primordial thyroid gland from the tongue

Normally the thyroglossal duct atrophies andNormally the thyroglossal duct atrophies and

disappear disappear

A remnant of it may persist and form a cyst in A remnant of it may persist and form a cyst in

the tongue or in the anterior part of the neckthe tongue or in the anterior part of the neck




SinusesSinuses It usually lies just inferior to the hyoid boneIt usually lies just inferior to the hyoid bone

Most thyroglossal duct cysts are observed by theMost thyroglossal duct cysts are observed by theage of 5 yearsage of 5 years

The swelling produced is usually develops as aThe swelling produced is usually develops as a

painless, progressively enlarging, moveablepainless, progressively enlarging, moveable

massmass

The cyst may contain some thyroid tissueThe cyst may contain some thyroid tissue




SinusesSinuses Following infection of a cyst, a perforationFollowing infection of a cyst, a perforation

of the skin occurs forming a thyroglossalof the skin occurs forming a thyroglossal

duct sinusduct sinus

It usually opens in the median plane of theIt usually opens in the median plane of the

neck, anterior to the laryngeal cartilagesneck, anterior to the laryngeal cartilages



Development of TongueDevelopment of Tongue

A median triangular elevation appears in the A median triangular elevation appears in the

floor of the primordium pharynx near the end of floor of the primordium pharynx near the end of

44thth

week, just rostral to the foramen cecumweek, just rostral to the foramen cecum

This swelling or median tongue bud is the firstThis swelling or median tongue bud is the first

indication of tongue developmentindication of tongue development

Soon two oval distal tongue buds develop onSoon two oval distal tongue buds develop on

each side of the median tongue budeach side of the median tongue bud




The three lingual buds result from theThe three lingual buds result from the

proliferation of mesenchyme in ventromedialproliferation of mesenchyme in ventromedial

parts of the first pair of pharyngeal archesparts of the first pair of pharyngeal arches

The distal tongue buds rapidly increase in size,The distal tongue buds rapidly increase in size,

merge with each other, and overgrow themerge with each other, and overgrow the

median tongue budmedian tongue bud

The merged distal tongue buds form the anterior The merged distal tongue buds form the anterior

twotwo--thirds (oral part) of the tonguethirds (oral part) of the tongue




Fusion of the distal tongue buds isFusion of the distal tongue buds is

indicated by a middle groove, the medianindicated by a middle groove, the median

sulcus of the tongue and internally by thesulcus of the tongue and internally by thefibrous lingual septumfibrous lingual septum

Median tongue bud forms no recognizableMedian tongue bud forms no recognizablepart of the adult tonguepart of the adult tongue



Formation of Posterior third of Formation of Posterior third of

TongueTongue

It is indicated by two elevations that developIt is indicated by two elevations that develop

caudal to the foramen cecumcaudal to the foramen cecum

Copula: Forms by fusion of the ventromedial partCopula: Forms by fusion of the ventromedial part

of the second pair of pharyngeal archesof the second pair of pharyngeal arches

The hypopharyngeal eminence: DevelopsThe hypopharyngeal eminence: Develops

caudal to the copula from mesenchyme in thecaudal to the copula from mesenchyme in the

ventromedial parts of the third and fourth pairs of ventromedial parts of the third and fourth pairs of

archesarches




TongueTongue

As the tongue develops the copula is gradually As the tongue develops the copula is graduallyovergrown by the hypopharyngeal eminenceovergrown by the hypopharyngeal eminence

and disappear and disappear

As a result, the pharyngeal part of the tongue As a result, the pharyngeal part of the tonguedevelops from the rostral part of thedevelops from the rostral part of the

hypopharyngeal eminencehypopharyngeal eminence

The line of fusion of the anterior and posterior The line of fusion of the anterior and posterior parts of the tongue is roughly indicated by a Vparts of the tongue is roughly indicated by a V--

shaped groove called terminal sulcusshaped groove called terminal sulcus




TongueTongue

Pharyngeal mesenchyme forms the connective tissuePharyngeal mesenchyme forms the connective tissueand vasculature of the tongueand vasculature of the tongue

Most of the tongue muscles are derived from myoblastsMost of the tongue muscles are derived from myoblaststhat migrate from the occipital myotomesthat migrate from the occipital myotomes

The hypoglossal nerve (CNThe hypoglossal nerve (CN ) accompanies the) accompanies the

myoblast during their migration and innervates themyoblast during their migration and innervates thetongue muscles as they developtongue muscles as they develop

The entire tongue is within the mouth at birth, itsThe entire tongue is within the mouth at birth, itsposterior third descends into the oropharynx by 4 yearsposterior third descends into the oropharynx by 4 years

of ageof age



Papillae and Taste BudsPapillae and Taste Buds

Lingual papillae appear towards the end of theLingual papillae appear towards the end of theeighth weekeighth week

The vallate and foliate papillae appear first,The vallate and foliate papillae appear first,close to the terminal branches of theclose to the terminal branches of theglossopharyngeal nerve (CNglossopharyngeal nerve (CN ))

The fungiform papillae appear later nearThe fungiform papillae appear later neartermination of chorda tympani branch of thetermination of chorda tympani branch of thefacial nervefacial nerve




The most common lingual papillae, known asThe most common lingual papillae, known asfiliform papillae because of their threadlikefiliform papillae because of their threadlikeshape, develop during early fetal period (10shape, develop during early fetal period (10--1111

weeks)weeks)

They contain afferent nerve endings sensitive toThey contain afferent nerve endings sensitive totouchtouch

Taste buds develop during 11Taste buds develop during 11--13 weeks13 weeks

Most taste buds form on the dorsal surface of Most taste buds form on the dorsal surface of

the tonguethe tongue




Fetal responses in the face can beFetal responses in the face can be

induced by bitter tasting substances at 26induced by bitter tasting substances at 26--28 weeks, indicating that the reflex28 weeks, indicating that the reflex

pathways between taste buds and facialpathways between taste buds and facial

muscles are established by this agemuscles are established by this age



Nerve Supply of the TongueNerve Supply of the Tongue

The development of tongue explains its nerveThe development of tongue explains its nerve

supplysupply

The sensory supply to the mucosa of almost theThe sensory supply to the mucosa of almost the

entire anterior twoentire anterior two--thirds of the tongue is fromthirds of the tongue is from

the lingual branch of the mandibular division of the lingual branch of the mandibular division of

the trigeminal nervethe trigeminal nerve

This nerve is the nerve of first pharyngeal archThis nerve is the nerve of first pharyngeal arch

and this arch forms the median and distaland this arch forms the median and distal

tongue budstongue buds




Facial nerve is the nerve of second pharyngealFacial nerve is the nerve of second pharyngealarcharch

Its chorda tympani branch supplies the tasteIts chorda tympani branch supplies the tastebuds in the anterior twobuds in the anterior two--thirds of the tonguethirds of the tongueexcept the vallate papillaeexcept the vallate papillae

The facial nerve does not supply any of theThe facial nerve does not supply any of thetongue mucosa, except for taste buds in the oraltongue mucosa, except for taste buds in the oralpart of the tonguepart of the tongue




The vallate papillae in the oral part of the tongueThe vallate papillae in the oral part of the tongueare innervated by glossopharyngeal nerve (CNare innervated by glossopharyngeal nerve (CN) of the third pharyngeal arch) of the third pharyngeal arch

This is due to the reason that mucosa of This is due to the reason that mucosa of posterior two third of the tongue is pulled slightlyposterior two third of the tongue is pulled slightlyanteriorly as the tongue developsanteriorly as the tongue develops

The posterior third of the tongue is innervatedThe posterior third of the tongue is innervatedmainly by the glossopharyngeal nerve, which ismainly by the glossopharyngeal nerve, which isa nerve of third pharyngeal archa nerve of third pharyngeal arch




The superior laryngeal branch of the vagusThe superior laryngeal branch of the vagusnerve (CNnerve (CN ) of the fourth arch supplies small) of the fourth arch supplies small

area of the tongue anterior to the epiglottisarea of the tongue anterior to the epiglottis

All muscles of the tongue are supplied by the All muscles of the tongue are supplied by the

hypoglossal nerve (CNhypoglossal nerve (CN ), except for ), except for palatoglossus, which is supplied frompalatoglossus, which is supplied from

pharyngeal plexus by fibers arising from thepharyngeal plexus by fibers arising from the

vagus nervevagus nerve

03-tongue & thyroid

Documents